Final answer:
The "choo choo" phenomenon is linked to social isolation in monkeys, signifying abnormal behaviors due to lack of social contact during development. Research by the Harlows accentuated the importance of social comfort over food among rhesus monkeys.
Step-by-step explanation:
The "choo choo" phenomenon is associated with D. Social isolation in monkeys. This term relates to the behavioral quirks and abnormalities observed in monkeys that have experienced severe forms of social deprivation during their development. Research on rhesus monkeys by Harry and Margaret Harlow demonstrated that deprivation of social contact, as opposed to physical or cognitive deprivation, can lead to significant emotional and social difficulties. Monkeys raised in isolation exhibited behavioral issues and failed to develop normal social interactions.
The Harlows' studies specifically highlighted the importance of social comfort over mere sustenance, as shown by monkeys' preference for a terrycloth 'mother' that provided no food but physical comfort over a wire mother that provided food but no comfort. This finding underlines the importance of social bonding and emotional contact in the development of social animals closely related to humans.